This patent application claims priority based on Japanese patent applications, H11-188829 filed on Jul. 2, 1999, H11-195254 filed on Jul. 9, 1999, and H11-207039 filed on Jul. 22, 1999, H11-209177 filed on Jul. 23, 1999, and H11-216731 filed on Jul. 30, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a glass base material, which is a base material of an optical fiber, manufacturing apparatus and a glass base material manufacturing method.
2. Description of the Related Art
There are several processes involved in the manufacture of an optical fiber. A gas material, which is a base material of an optical fiber, is hydrolyzed and formed into a glass base material. The glass base material is sintered to form an optical fiber preform, which is drawn to form an optical fiber.
There are several methods for manufacturing a glass base material. As one of the methods for manufacturing a glass base material, there is an OVD method, that is, an outside vapor deposition method. In the OVD method, a gas material is hydrolyzed by a burner to form glass particles which form the base material of the optical fiber. The glass particles are accumulated around and along a base rod, which is rotated at a constant speed, and the accumulated glass particles become a glass base material.
To increase the productivity of manufacture of glass base materials, a plurality of burners are used for hydrolyzing the gas material. The plurality of burners are moved back and forth along the longitudinal direction of the base rod, in order to form a glass base material having a constant diameter. The turning point of the back and forth movement of the burners needs to be dispersed evenly along the longitudinal direction of the base rod, so that the diameter of the glass base material accumulated by the burners can be constant for substantially the whole length of the glass base material.
There is a method of controlling the position of the turning point by using software that calculates the position of the turning point of the burners. To control the turning point to be a predetermined position, several steps have to be executed.
However, the method of controlling the turning points using software causes a delay in the movement of burners, because it takes time for the software to calculate the turning point and also takes time to provide the calculated turning points to the unit that moves the burners. The burners pass over the turning point which is to be calculated by the software and provided to the unit which moves the burners. Therefore, the diameter of the glass base material becomes uneven and the roughness of the surface of the glass base material increases. Therefore, the quality of the glass fiber drawn from the glass base material having an uneven diameter, decreases.
Therefore, it is an object of the present invention to provide an apparatus for glass base material manufacturing and a method for glass base material manufacturing which overcomes the above issues in the related art. This object is achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.
According to the first aspect of the present embodiment, an apparatus for manufacturing a glass base material, which is a base material of an optical fiber, can be provided. The apparatus may comprise a base rod, around and along which the glass base material may be formed; a burner that hydrolyzes and accumulates a gas material, which is a base material of the glass base material, around and along the base rod; a first burner-moving-unit that moves the burner in a direction parallel with a longitudinal direction of the base rod; and a second burner-moving-unit that moves the first burner-moving-unit in the same moving direction of the first burner-moving-unit.
The first burner-moving-unit may move the burner back and forth in the direction parallel with a longitudinal direction of the base rod. The second burner-moving-unit may move the first burner-moving-unit back and forth in the same movement direction as the first burner-moving-unit.
The first burner-moving-unit may move the burner at a first cycle, and the second burner-moving-unit may move the first burner-moving-unit at a second cycle, which is different from the first cycle. The first cycle maybe shorter than the second cycle, may be an integer multiple of the second cycle, and may be synchronized with the second cycle.
The apparatus may further comprise a plurality of burners arranged parallel to the longitudinal direction in the first burner-moving-unit. Each of intervals between the plurality of burners may be substantially constant. Each of the plurality of burners may accumulate in each different region, which is a part of the length of a whole length of the glass base material.
The first burner-moving-unit further may have a first shaft, along which the first burner-moving-unit moves, and the second burner-moving-unit further may have a second shaft along which the first burner-moving-unit moves. The first burner-moving-unit may have a first motor, which rotates the first shaft, and the second burner-moving-unit may have a second motor which rotates the second shaft.
A moving range of at least one of the first burner-moving-unit and the second burner-moving-unit may be an integer multiple of each of the intervals between the plurality of burners. The integer may be an integer which does not exceed a number of the plurality of burners divided by five. The integer may be the integer xe2x80x9c1xe2x80x9d.
The apparatus may further comprise a chamber, which accommodates the base rod, the burner, the first moving unit, and the second moving unit, and includes a duct that vents exhaust from inside the chamber, provided in the longitudinal direction of the base rod for substantially the whole length of the chamber.
The chamber may have a tube shape running in the longitudinal direction, parallel to the base rod, both ends of which are closed. A cross section of the tube shape may be polygonal or a cylindrical shape. The duct may be provided on the top of the chamber. The duct may include a vent plate having a plurality of vents for substantially the whole length of the chamber. The plurality of vents may be provided at a constant interval. The vent plate may include a vent controller which controls airflow of the plurality of vents.
The chamber may further include a plurality of the ducts provided on the chamber, and the ducts may face an outlet of the burner located over the base rod. The chamber may include a base having a flow regulating structure which intakes outside air, thus regulating airflow flowing from the base to the duct. The flow regulating structure may be made of a filter. The filter may be made of a non-woven fabric. The filter may have an accordion shape. The flow regulating structure may be formed by a plate having a plurality of air holes.
The base rod may have a pair of dummy rods provided on both ends of the base rod, and the diameter of the dummy rod, D, and the weight of the glass base material, W, may have a relationship of 0.13xe2x89xa6D/W0.5. The diameter of the dummy rod, D, and the weight of the glass base material, W, may further have a relationship of 0.13xe2x89xa6D/W0.5xe2x89xa60.25.
According to the second aspect of the present embodiment, a method for manufacturing a glass base material, which may be a base material of an optical fiber, comprises: rotating a base rod, around and along which the glass base material may be formed; hydrolyzing and accumulating a gas material, which is a base material of the glass base material, around and along the base rod using a burner; and the hydrolyzing and accumulating includes: moving the burner at a first cycle, in a direction parallel with a longitudinal direction of the base rod; and moving a unit, which moves the burner at the first cycle, at a second cycle in the same movement direction as the movement of the burner.
Moving the burner may move the burner back and forth in a direction parallel with the longitudinal direction of the base rod, and furthermore, the moving the unit may move the unit back and forth in the direction parallel with the longitudinal direction of the base rod.
The first cycle may be different from the second cycle, and may be shorter than the second cycle. The first cycle may be at integer multiple of the second cycle, and may be synchronized with the second cycle.
Hydrolyzing and accumulating may be performed by a plurality of the burners. Each of the plurality of the burners may be provided along the longitudinal direction of the base rod at a substantially constant interval. The hydrolyzing and accumulating process may accumulate the glass base material using each of the plurality of burners, and each of the plurality of burners may accumulate the gas material for each different region, which is a part of the length of the whole length of the base rod.
Moving the burner may move the burner for a distance which is an integer multiple of the interval, or moving the unit may move the unit for a distance which is an integer multiple of the interval. The integer may not exceed a number of the plurality of burners divided by five. The integer may be the integer xe2x80x9c1xe2x80x9d.
The hydrolyzing and accumulating may accumulate the gas material in a chamber accommodating the base rod, the glass base material, the burner and the unit; and the hydrolyzing and accumulating may include controlling airflow which flows through the chamber. The controlling the airflow may include exhausting gas inside the chamber through a duct provided on the chamber for substantially the whole length of the chamber along the longitudinal direction of the base rod.
Controlling the airflow may further include exhausting the inside gas from a plurality of ducts provided on the chamber, the plurality of ducts facing an outlet of the burner across the base rod for substantially the whole length of the chamber along the longitudinal direction of the base rod. The exhausting may include exhausting the gas from inside the chamber through a vent plate, which has a plurality of vents provided for substantially the whole length of the chamber at a constant interval. The control of the airflow may include regulating airflow that flows from the base of the chamber. The regulating of the airflow may filter outside air.
The method may further comprise cooling the glass base material, which is accumulated by the hydrolyzing and accumulating, by controlling a surface temperature of the glass base material. The cooling may control a cooling speed for decreasing the surface temperature of the glass base material. The cooling may control the cooling speed to be slower than 30xc2x0 C. per minute for a predetermined time after the hydrolyzing and accumulating is finished. The predetermined time may be ten minutes.
The hydrolyzing and accumulating may accumulate the gas material so that the relationship between the diameter of a pair of dummy rods provided on both ends of the base rod for holding the base rod, D, and a weight of the glass base material, W, may become 0.13xe2x89xa6D/W0.5. The hydrolyzing and accumulating may accumulate the gas material so that the relationship between the diameter of the pair of dummy rods, D, and the weight of the glass base material, W, may become 0.13xe2x89xa6D/W0.5xe2x89xa60.25.
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.